DESCRIPTION (Taken from application) Toxicity due to exposure to high levels of arsenic through dietary, occupational, or medicinal routes has been well documented in different countries. The most obvious and prevalent manifestations of arsenic toxicity are the cutaneous changes that involve hyperkeratosis and increased pigmentation, and latent basal and squamous cell carcinoma. The latter two types of skin cancer differ from the sun induced skin cancer tumors in that they occur mainly on the palms and soles, rather than on sun exposed anatomical sites, and are more invasive and metastatic. Although arsenic induced cutaneous alterations are histologically well characterized, the molecular mechanisms by which they arise are poorly understood. In particular, the mechanisms by which arsenic affects genomic DNA and induces the expression or suppression of specific genes are for the most part unknown. Given that the skin is the first interface between the human body and the environment, and that cutaneous manifestations often reflect internal organ dysfunction, it is important to elucidate the mechanism of action of arsenic on human skin. There is sufficient evidence to support the notion that arsenic induces oxidative stress in mammalian cells. In the cutaneous epidermis, increased keratinocyte proliferation that leads to hyperkeratosis and eventually cancer tumors, as well as hyperpigmentation, may be the outcome of arsenic induced oxidative stress in keratinocytes and melanocytes, respectively. We are proposing to investigate the hypothesis that arsenic induced cutaneous alterations result from oxidative stress that disrupts normal epidermal cell proliferation and differentiation. For this, we will use primary cultures of normal human melanocytes and keratinocytes, as well as a skin substitute model that mimics the skin in situ. The effects of arsenic on genes involved in regulating keratinocyte proliferation and differentiation, and melanocyte pigmentation will be elucidated. The above in vitro models represent an optimal approach to elucidate the mechanism of action of arsenic on human cells and tissues. The results to be obtained should be relevant to other epithelial tissues, such as lung and bladder tissues, that are affected by arsenic. The studies hereby proposed should set the stage for further investigations of the mechanisms by which arsenic might promote the effects of other environmental carcinogens, such as ultraviolet radiation and polycyclic aromatic hydrocarbons. The outcome of this proposal should lead to more effective means for intervening in, and treating the manifestations of arsenic toxicity, and for setting more effective policies regarding safe levels of arsenic exposure.